1. Field of the Invention
The present invention relates, in general, to solenoid valves of electronically controlled brake systems for automobiles and, more particularly, to a device for stably and securely mounting the coil assemblies of such solenoid valves in the electronic control unit""s housing of such a brake system.
2. Description of the Prior Art
In the prior art, several types of electronically controlled brake systems for automobiles have been proposed and used. Examples of such electronically controlled brake systems are an anti-lock brake system (ABS), a brake traction control system (BTCS), and a vehicle dynamic control system (VDCS). The ABS electronically controls oil pressure fed to wheel brakes and prevents slippage of wheels during a braking operation. The BTCS is designed to appropriately lock the drive wheels at high speeds or during sudden acceleration, thus preventing slippage of the drive wheels. The VDCS is fabricated by a combination of the ABS and BTCS, and controls braking oil pressure to secure traveling stability while driving an automobile.
A conventional electronically controlled brake system consists of a plurality of solenoid valves, which control a flow of pressurized oil fed to the hydraulic brakes provided at the wheels. The brake system also has a low-pressure accumulator, which temporarily stores pressurized oil drained from the brakes during a braking operation in a pressure reducing mode. An oil pump forcibly sucks the pressurized oil from the low-pressure accumulator, and outputs the oil. A high-pressure accumulator is arranged at the outlet of the oil pump, and reduces pressure pulsation of oil outputted from the pump. The brake system also includes an electronic control unit (ECU), which controls the operation of the pump and solenoid valves.
In the conventional electronically controlled brake system, the valve assemblies of the solenoid valves, oil pump, low- and high-pressure accumulators are compactly set in a modulator block made of aluminum. The ECU is fabricated by setting the solenoid valve""s coil assemblies and a circuit board in a housing. This ECU is integrated with the modulator block into a single body using mounting bolts. FIG. 1 shows a conventional structure for mounting the solenoid valves of an electronically controlled brake system.
In a conventional electronically controlled brake system, the valve assemblies 2a of the solenoid valves 2 are compactly set in a modulator block 1, while the coil assemblies 2b of the solenoid valves 2 are securely set in an ECU 3.
The ECU 3 consists of a housing 3a, which is a rectangularly walled body made of a plastic material through a plastic injection molding process. This housing 3a is mounted to the modulator block 1 using a plurality of mounting bolts 3c. A circuit board 3b is set in a space independently defined in the lower portion of the housing 3a. The coil assemblies 2b of the solenoid valves 2 are set in the main cavity of the housing 3a. Each of the coil assemblies 2b consists of a cylindrically coiled coil 2c, and two lead wires 2d electrically connecting the coil 2c to the circuit board 3b. When the ECU 3 is assembled with the modulator block 1 into a single body, the projecting ends or the sleeves of the valve assemblies 2a are smoothly inserted into the central bores of the coil assemblies 2b, respectively, with a clearance formed between the sleeves and the bores. When a current is applied to the coil assemblies 2b of the solenoid valves 2 after assembling the ECU 3 with the modulator block 1 into a single body, electric fields are formed at the coil assemblies 2b and selectively open or close the valve assemblies 2a of the solenoid valves 2.
In the conventional structure, the coil assemblies 2b of the solenoid valves 2 are fixed at their lower ends in the housing 3a of the ECU 3 by a coil mounting member 4, which is produced through an over-molding of rubber. That is, the coil assemblies 2b are securely fixed at their lower portions to the bottom of the ECU""s housing 3a while being molded with a xe2x80x9cmolderxe2x80x9d which is a kind of rubber. The valve assemblies 2a of the solenoid valves 2, which are set in the modulator block 1, are inserted into the central bores of the coil assemblies 2b. 
However, the conventional structure for mounting the solenoid valve""s coil assemblies 2b in the ECU""s housing 3a is problematic in that the mounting of the coil assemblies 2b in the housing 3a is accomplished by the coil mounting member 4 made of rubber. Therefore, it is difficult to mount the coil assemblies 2b in the housing 3a, in addition to lengthening the processing time while mounting the assemblies 2b. In addition, a facility for injecting the molder to form the coil mounting member 4 must be added to the assembling line of ECUs 3, thus forcing the manufacturer of electronically controlled brake systems to pay excessive money for installing the facility. This increases the production cost of such brake systems.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a coil assembly mounting device, which has an improved structure capable of more easily mounting the coil assemblies of solenoid valves in an ECU""s housing of an electronically controlled brake system for automobiles, and which reduces the production cost of such brake systems.
In order to accomplish the above objects, the present invention provides in a solenoid valve for electronically controlled brake systems, comprising a valve assembly having an armature movably set in a sleeve; a coil assembly set in a housing of an electronic control unit of a brake system and having a bobbin axially receiving the sleeve of the valve assembly, with a coil wound around the bobbin; a lead wire inserted in the bobbin and connected to a circuit board set in the housing of the electronic control unit; and a device for mounting the coil assembly in the housing of the electronic control unit, the device comprising: a through hole formed in the bottom wall of the housing of the electronic control unit; and a boss axially extending downward from the bottom of the bobbin at a position around the edge of the bobbin, and inserted into the through hole to be set in the hole.
In the device, the boss passes through the through hole to be exposed outside the hole at an end thereof, and plastically deformed at the exposed end to form a stopper preventing an undesired removal of the coil assembly from the bottom wall of the housing.
The lower end of the through hole is gradually enlarged in its diameter in a direction from the top to the bottom, thus forming a flared end allowing the stopper to be easily formed.
In the device, a cylindrical holder is formed in the housing, and receives the coil assembly therein, with the through hole formed on the bottom wall of the cylindrical holder.
The device further comprises: an additional boss axially extending downward from the bottom of the bobbin at a position around the edge of the bobbin, with the lead wire inserted into the additional boss; and a mounting hole formed on the bottom wall of the cylindrical holder, and receiving the additional boss therein.